Interpretation of regional fold interference structures in SE Norway based on comparison with model experiments

Abstract

The Röefmskog region of south-east Norway consists of Proterozoic gneisses; the youngest are c. 1275 Ma red orthogneisses which intruded, probably in a sheet-like fashion, c. 1630 Ma grey orthogneisses and still older gneisses. The area was deformed in three phases during the Sveconorwegian orogeny. The first phase produced a penetrative, but more or less well-developed, foliation and concordant migmatite schlieren. The next deformation phase produced roughly E-W folds, while during the last deformation phase roughly NW-SE folds were superimposed. Several orders of folds were produced in both fold phases.

Map-scale interference structures are outlined by the boundary of the red orthogneisses. Each of the fold sets, as well as the interferences between them, shows similarities to buckle folds and buckling interference patterns that were produced experimentally by layer-parallel shortening and reported by several authors.

A Plasticene model of the map-scale folds was constructed to illustrate the interpretation of the superposed structures, and these were compared with experimentally derived structures and classified according to the buckling modes distinguished by Ghosh et al. (1992).

Acknowledgements: The field-work in the Römskog area was supported by the Danish Natural Science Research Council and by the Geological Survey of Norway. Thanks are due to René Madsen who drafted the figures, to Lars Frimodt Pedersen who computer-contoured Figure 22.3, and to John Bailey who improved the English text.